1. Field of the Invention
The present invention relates to a fluid filled vibration damping device capable of exhibiting damping effect based on flow action of a sealed non-compressible fluid flowing through an orifice passage connecting between a pressure-receiving chamber and an equilibrium chamber, and to a method of producing the same.
2. Description of the Related Art
Fluid filled vibration damping devices capable of exhibiting vibration damping effect based on resonance or other flow action or behavior of a non-compressible fluid sealed therein are known in the art, as vibration damping devices, such as vibration damping support or vibration damping couplings, intended for installation between components that make up a vibration transmission system. JP-A-06-341483 discloses one example of the vibration damping device of this kind, wherein a first mounting member is positioned next to one opening of a second mounting member of tubular shape, and the first mounting member and second mounting member are elastically connected by a main rubber elastic body. The device is used as an automotive engine mount, for example.
In this type of fluid filled vibration damping device, the other opening of the second mounting member of tubular shape is fluid-tightly closed by a flexible rubber film, thereby forming a fluid sealing area between opposing faces of the main rubber elastic body and the flexible rubber film. Typically, the fluid sealing area is partitioned by means of a partition member supported by the second mounting member, thereby forming a pressure-receiving chamber whose wall is partially defined by the main rubber elastic body, and an equilibrium chamber whose wall is partially defined by the flexible rubber film, while an orifice passage permitting a fluid communication between the pressure-receiving chamber and the equilibrium chamber. With this arrangement, upon input of vibrational load between the first and second mounting members, relative fluid pressure fluctuation will be induced between the pressure-receiving chamber and the equilibrium chamber. In accordance with this fluid pressure fluctuation, the fluid is forced to flow through the orifice passage between the two chambers, thereby exhibiting vibration damping effect based on resonance or flow action of the fluid.
In recent years, for the purpose of enhancing vibration damping capability of the fluid filled vibration damping device of such construction, there has been proposed to provide a cover metal member for covering an external surface of the flexible rubber film, to thereby form a tightly closed air chamber on one side of the flexible rubber film opposite from the equilibrium chamber. More specifically, it has been attempt to utilize the thus formed tightly closed air chamber to control a ratio of a static spring constant and a dynamic spring constant of the vibration damping device by means of air spring action generated by the tightly closed air chamber.
The aforementioned document No. JP-A-06-341483 discloses a specific structure wherein an outer rim of the cover metal member (i.e., air-tight plate) is fixedly caulked against the second mounting member (support tube) together with an outer rim of the flexible rubber film (diaphragm).
However, the proposed assemble structure through caulking process together with the flexible rubber film, makes it difficult to conduct the assembly of the flexible rubber film within a mass of the non-compressible fluid, causing traverse effect for filling the fluid to the fluid sealing area. More specifically described, if you try to fix the flexible rubber film and the cover metal member by caulking, it is difficult to prevent entry of the fluid into the tightly closed air chamber. This drawback needs an additional special operation, e.g., for draining the fluid entered into the tightly closed air chamber via a drain port after the caulking fixation process, and closing the drain port by means of rivet or the like, as taught in JP-A-2003-206976.
To cope with this problem, the present assignee has been proposed in his prior U.S. patent application that has been issued as a U.S. Pat. No. 5,628,498, a technique wherein after the pressure-receiving chamber and the equilibrium chamber are filled with the non-compressible fluid, a metallic bracket of cup shape having a bottom is press fitted onto the fluid-filled vibration damping device, so that a bottom portion of the metallic bracket is closed by means of the flexible rubber film, thus forming the tightly closed air chamber.
However, the proposed construction of the fluid filled vibration damping device requires the metallic bracket having the bottom, providing adverse influence on the manufacturing efficiency in the coating process or the like. Namely, the metallic bracket needs to be subjected to the coating process for the purpose of rust proofing or corrosion proofing. The metallic bracket having the bottom may be coated by drenching or spraying. This is likely to cause an undesirable remain of coating on the bottom of the metallic bracket, inevitably needing cumbersome treatments for removing the coating.
Furthermore, Since the metallic bracket is not suitable for drawing process, due to its shape or strength, it may be fixed to the fluid filled vibration damping device by press fitting. However, the fixation structure by means of press fitting is likely to cause damage of the sealing rubber upon pressing, for example.